The present invention relates to a control device for an internal combustion engine for detecting a knocking state produced in the engine and for feedback controlling an ignition timing, etc. of the engine in response to the knocking state.
It is known that a continuous and strong knocking state adversely affects the durability of an engine, but that a slight knocking state at relatively low engine speed ranges improve fuel consumption and output power characteristics of the engine. Further, it is known that the ignition timing is closely related to the occurrence of the knocking, in general the more the ignition timing is advanced the more knocking tends to occur.
Accordingly, a device has been proposed in which, in order to improve fuel consumption and output power characteristics of an engine, a knocking state produced in the engine is detected and the ignition timing is advanced and retarded in response to the detected knocking state so as to maintain a slight knocking state in the engine.
In such a known device, however, it takes a certain time to actually control the ignition timing in response to the detected knocking state, because the feedback control system thereof has a certain delay time in its response characteristic, so that only for a knocking state changing more slowly than the delay time can the ignition timing be smoothly controlled at an optimum timing.
In a transitional driving condition in which the driving condition of the engine is suddenly changed, the knocking state is also suddenly changed accordingly. However, due to the delay time the ignition timing cannot be controlled as quickly as desired in response to the sudden change of the knocking state. Under such transitional driving conditions optimum control of the ignition timing can not be obtained by conventional devices.
Since the knocking state tends to be enhanced in the transitional driving condition, more particularly during accelerating conditions, the ignition timing should be retarded as quickly as possible. However, in known devices, in order to stabilize the control or to prevent hunting, the ignition timing is retarded by a predetermined amount at a predetermined engine speed and therefore cannot be retarded quickly by the required amount. Therefore, the ignition timing cannot be controlled in an optimum manner by conventional devices, particularly during rapid acceleration conditions.
Therefore, during rapid acceleration condition the firing condition and hence fuel consumption and output power characteristics of the engine deteriorates.